A resin concrete pipe comprises an aggregate and a resin material and is superior in strength and corrosion resistance. Further, by forming a resin layer on the inner peripheral side and/or the outer peripheral side of a resin concrete layer there can be obtained a composite pipe more superior in corrosion resistance. Usually, a centrifugal molding method is used for producing a composite pipe having a resin concrete layer, which pipe will hereinafter be referred to sometimes merely as a "composite pipe", and for producing a resin concrete pipe. According to the centrifugal molding method, material is poured into a pipe forming outer mold while the outer mold is rotated about the axis thereof, and is formed into the shape of a pipe, which is then solidified and thereafter taken out from the pipe forming outer mold. In the centrifugal molding method, however, low productivity occurs be discussed later.
For forming a resin concrete layer in the pipe forming outer mold, various material feeding devices have been used, and there are known 1 a method wherein a resin material consisting of a resin and a hardening agent and an aggregate are fed from separate nozzles, and 2 a method wherein a resin concrete material is obtained by mixing an aggregate and a resin material in advance and is then transferred up to a front end portion of a material feeding device and fed. For example, the above method 1 is disclosed in Japanese Patent Publication No. 45923/86. In the case where a composite pipe 1 having resin layers 2 and 4 of the same composition formed on the inner and outer peripheral surfaces of a resin concrete layer 3, such as that shown in FIG. 3, is to be produced by the technique disclosed in said patent publication, there is used such a material feed arm as illustrated in FIG. 5. As shown therein, successively from a front end side of a material feed arm portion 50 there are disposed a first resin material feed portion 51, a chopped strand feed portion 52, a second resin material feed portion 53, a sand conditioning portion 54 and a sand feed portion 55. According to this method, a first resin material 61 and chopped strands 62 are fed to form an outer periphery-side resin layer 2, then a second resin material 63 and sand 64 are fed in this order, during forward movement of the material feed arm 50. During backward movement of the arm, as shown in FIG. 6, a sand conditioning plate 56 of the sand conditioning portion 54 extends and conditions an uneven surface of the sand to form a resin concrete layer 3, thereafter the chopped strands 62 and the first resin material 61 are fed to form a inner periphery-side resin layer 4.
The centrifugal molding method aims at forming layers each of uniform thickness while utilizing a centrifugal force created by the rotation of a mold. But in the method wherein sand and resin material are fed separately in forming a resin concrete layer, as mentioned above, the resin material and the aggregate are apt to be separated from each other due to a difference in specific gravity, resulting in that the combined use of both materials is not fully effective. Besides, since the aggregate is present on the inner surface side of pipe, the pipe inner surface does not become flat and there are formed concave and convex portions, as shown in FIG. 5. To avoid this inconvenience, it is necessary to level the pipe inner surface by using such a sand conditioning plate such as illustrated in FIGS. 5 and 6, resulting in productivity being deteriorated markedly.
Even if the pipe inner surface is levelled by the sand conditioning plate 56 or the like, it is difficult to obtain a uniform and smooth surface, and there remain uneven portions. In forming a resin layer over the whole surface of the concrete layer, therefore, there arises the problem that the amount of resin used becomes larger than necessary.
Also, as for the above method 1, Japanese Patent Laid Open No. 246704/87 discloses a method wherein first an aggregate is fed and then a liquid resin is fed. According to this method, however, a centrifugal force as large as 50G or so is required for impregnating the resin into the aggregate. Moreover, there are limitations on the thickness and grain size of the aggregate layer which permit the impregnation of resin therein, and in some particular thickness of a resin concrete layer in a composite pipe to be produced, it is required to repeat the aggregate feeding step and the resin impregnating step several times.
On the other hand, the foregoing method 2 is disclosed in Japanese Patent Laid Open No. 42207/89. In the conventional methods which had been known before the method 2, a resin concrete containing a room-temperature hardening agent adheres to a mixing machine and a material introducing device and solidifies, thus requiring a longer time for cleaning than for centrifugal molding. Taking note of this point, method 2 employs a thermosetting agent in place of said room-temperature hardening agent to prevent a resin concrete material from solidifying at room temperature, thereby facilitating the cleaning work. According to this method, however, although the solidification of resin can be prevented, it is necessary, after solidifying a pipe inner layer on a centrifugal molding apparatus, to transfer the pipe into a heating chamber and harden the pipe body portion, thus resulting in productivity being deteriorated markedly.